clitellum 



Figure 1. — A microdrile. 



and passes upwards on either side of tlie pharynx 

 to, or just posteriorly to, the ])eristomium where 

 it joins a dorsal bilobed cerebral ganglion (or 

 brain). The gut begins as a short narrow- 

 esophagus, then widens into a simple tube (con- 

 stricted by the septa dividing each segment) 

 which extends throughout the body length. Just 

 posteriorly to the esophagus, the Enchytraeidae, 

 Naididae, and Tubificidae (microdriles) possess 

 a thickened pad of cells dorsally (the pharynx) 

 which can be extruded through the mouth and 

 to which, presumably, food particles adhere. In 

 the Megascolecidae (megadriles) a muscular 

 thickening of the gut wall, the gizzard, is usually 

 situated near the anterior end of the esophagus. 

 In the microdrile families bundles of darkly 

 staining secretory cells, the pharyngeal glands, 

 are found associated with the septa and gut in 

 the region of segments III to VII. In Tubificidae 

 and Naididae these glands are usually diffuse 

 cell masses located laterally and dorsally, or dor- 

 sally, to the gut. In Enchytraeidae, however, 

 the pharyngeal glands are discrete organs with 

 a characteristic appearance and distribution. 

 Peptonephridia, found only in some genera of 

 Enchytraeidae, are also glandular organs asso- 

 ciated with the anterior part of the gut; the term 

 is used in the sense of Nielsen and Christensen 

 (1959) to denote paired, tubular diverticulae 

 which arise at the esophageal-pharyngeal junc- 

 tion. The vascular system consists of dorsal and 

 ventral blood vessels which are connected in each 

 segment either directly by dorsoventral commis- 

 sures or indirectly through a blood plexus sur- 

 rounding the gut. Excretion is by means of seg- 

 mentary arranged paired nephridia. Each 



nephridium consists of a ciliated funnel which 

 o])ens in the coelom, and a convoluted tubule 

 which communicates with the exterior through 

 a nephridiopore located ventrally on the adja- 

 cent posterior segment. Nephridia are usually 

 absent in a variable number of anterior seg- 

 ments, in the region of the genitalia, in some 

 posterior segments, and in some species they 

 may be reduced to one, or a few, in number. 

 The coelom is usually a simple cavity filled with 

 coelomic fluid ; in some genera and species the 

 latter contains large numbers of coelomocytes 

 which are large, spherical to ovoid, free cells. 

 The genital system consists basically of male, 

 female, and spermathecal components. The male 

 component consists of one or two, rarely more, 

 pairs of testes whose products (sperm) are con- 

 ducted to the exterior by a more or less complex 

 set of male genitalia. The sperm from each pair 

 of testes is collected by a pair of male funnels 

 (located on the posterior septum of the testis seg- 

 ment) which each open into a tubular vas de- 

 ferens. The latter usually join paired ectoder- 

 mal storage and intromittant organs (the atria 

 and penes), or only one of these, which open 

 to the exterior through the male pores (see also 

 Fig. 2 and under "microdriles" and "Megasco- 

 lecidae" below) . The female system is composed 

 of one or two pairs of ovaries and small female 

 funnels which are situated ventrolaterally just 

 posteriad to the last testes segment. The sper- 

 mathecal component, whose function is to store 

 sperm after copulation, consists typically of a 

 pair of ectodermal pouches, the spermathecae, 

 which are located near the region of the gonads 

 (except in the Enchytraeidae where they are 



